We have recently developed and characterized an in vivo clonal assay system for normal parenchymal hepatocytes. This is presently the only method which can be utilized to precisely quantify both the probability of survival and neoplastic transformation after hepatocyte exposure to genotoxic agents. Cell survival will be determined by comparing the clonal growth of unexposed and carcinogen exposed hepatocytes after transplantation into the dorsal fat pads of hepatectomized syngeneic rats. The chemical carcinogenesis studies entail the adaptation of existing initiation-promotion protocols to the transplantation system, and the subsequent observation for enzyme altered foci (e.g. GGT positive) or hepatocellular carcinomas. Three chemical carcinogens will be used in comparative studies. They come from three different chemical classes, and though they all are metabolically activated by the liver, two are potent hepatocarcinogens (AAF, DENA) while BP is only weakly carcinogenic for the liver. Specifically we propose to: 1) compare the growth stimulation of initiated hepatocytes by the various promotion protocols, 2) estimate the transformation frequency on a per surviving rather than exposed cell basis, and 3) correlate both the cell survival and transformation data with the total and specific carcinogen adducts bound to the DNA. The results of these studies will enable us to quantitate the relative importance of initiation and promotion in hepatocarcinogenesis, thus allowing for a better understanding of the biology of hepatic neoplasia.